Non-woven webs of fabric having a variable thickness are known in the art. U.S. Pat. No. 3,402,227 dated Sept. 17, 1968 discloses a process for preparation of such non-woven webs from continuous filaments. Also the use of non-woven fabric on earthen surfaces to spread the stress from road or railway communication routes over a wider area, are likewise known in the art, with such fabric being formed, for instance, of polyester, and having the ability to filter out fine soil particles that would or could otherwise contaminate the track ballast, and also possessing the capability of passing water through the mat so as to actually aid in drainage of water from the soil beneath the mat. U.S. Pat. No. 3,670,506 dated June 20, 1972 and entitled Process For Stabilizing Soils, is directed to a method of utilizing non-woven fabric in poor support areas. Also, the use of mats for protecting bridge decks in a railroad environment are known such as for instance from U.S. Pat. No. 3,587,964 dated June 28, 1971.
Also in U.S. Pat. No. 3,598,680 dated Aug. 10, 1971 there is disclosed an air laying apparatus for making a web or pad of fiberous material with a predetermined non-uniform thickness configuration.
However, to applicant's knowledge, there has never been provided a variable thickness mat for use at stress transition zones in railroad track, and operable to progressively absorb and more evenly spread the stress from wheeled traffic at such zones, over wider areas.
Changes often occur in a railroad track bed's stability and its response to rail loads. These changes are especially detrimental to track stability at stress transition zones such as at track crossing diamonds, switches, car retarders, and the like. Rail and track structure damage may occur when abrupt changes in track structure responses exist as the track structure passes through these high stress zones.
The present mat invention provides an arrangement that changes in mat thickness along its length, and more evenly distributes the loads to the bearing soil as the train vehicle approaches and pass over these high stress regions. Thus as the train or railroad vehicles start their approach into a high stress track region, the fabric mat is relatively thin where the transition stresses are less, and the mat becomes thicker as the track structure stresses increase. Also, with the mat possessing high liquid conducting capabilities, the presence of water is reduced at the bearing ground areas, which further aids in the stability of the track structure, and the reduction of stresses applied thereto.